How many pencils would it take to build a one-man raft? Guess The Question How many pencils would it take to build a one-man raft? Pencils are usually made of a combination of cedarwood and a graphite/clay mixture, with a combined density of 0.6g/cm3 The average person weighs about 70kg. Volume of a pencil: 16 x pi x 0.4^2 = 0.64 pi cubic centimetres. Weight = 0.6 x 0.64 pi grams. Buoyancy = 0.4 x 0.64 pi grams = 0.256 pi grams. To hold up 70,000 grams, 70,000 / 0.256 pi = 87,038 pencils. Pencils are roughly cylindrical, about 16cm long and 8mm across.

The Answer 145,000 pencils per person ≈ £14,500 ≈ 3 Jet-Skis Density = 0.6g/cm3 Volume = 1.6 x π x 0.42 ≈ 0.80cm3 70,000 ÷ 0.48 ≈ 145,000 pencils Volume of a pencil: 16 x pi x 0.4^2 = 0.64 pi cubic centimetres. Weight = 0.6 x 0.64 pi grams. Buoyancy = 0.4 x 0.64 pi grams = 0.256 pi grams. To hold up 70,000 grams, 70,000 / 0.256 pi = 87,038 pencils. Weight = D x V = 0.48g